Human Rights Watch (HRW) on Friday decried what it called the "alleged mistreatment" of detainees, including children, by security forces in Zamboanga City in the southern Philippines.

The New York-based rights group said it had received reports of authorities beating and mistreating suspected Moro National Liberation Front (MNLF) fighters arrested during and after three weeks of fighting in the city.

“The Philippines government should promptly investigate all credible accounts of detainee mistreatment, take appropriate action to stop it and punish those responsible," HRW Asia director Brad Adams said in a statement.

The government has detained dozens of suspected Islamic militants since fighting began in the city on September 9, when MNLF fighters took over five coastal villages in Zamboanga and seized dozens of local people as hostages.

Sporadic fighting has continued although all of the hostages have been released.

As of Tuesday, there were 277 suspected MNLF fighters in custody, including six children under the care of the social welfare office.

So far, 97 of these detainees had been charged with rebellion, while charges are pending against the others.

The fighting killed 202 rebels, soldiers, and civilians, displaced nearly 120,000 people, and resulted in the destruction of more than 10,000 homes.

It is alleged the detainees had limited or no access to lawyers and family members, HRW said. Police and military personnel interrogate detainees without the presence of legal counsel, a violation of Philippines and international law guaranteeing legal representation, the rights group added.

International law prohibits torture and other cruel, inhuman or degrading treatment of people in custody. Individuals apprehended by the government should be promptly brought before a judge and charged with a credible criminal offense or released, the HRW statement said.

"The Philippines government has an obligation to conduct its investigations of rebel suspects in a transparent manner that respects due process and the rights of the accused to meet with lawyers and family members," Adams said.

HRW also reported that several people from five affected villages where the fighting was heaviest remain unaccounted for and are considered missing. It is not known if those missing individuals were among the detained suspects.

A military spokeman expressed surprise at HRW's allegations, saying that any soldiers found to have committed violations will be tried by court martial.

He said the military is open to any inquiry into the Zamboanga fighting and subsequent detentions.

"We have sacrificed a lot of our soldiers in this fight and to us really, if the public needs to know more about our operations, then we will make it available. We never tried to hide anything from the beginning," he said.

The country's human rights commission meanwhile, said it will investigate any alleged human rights abuses committed after the standoff.

"We will look into the [Human Rights Watch] report," said commission head Loretta Ann Rosales.

In a Twitter post earlier, Rosales had congratulated the "brave police and soldiers" whom she said contained the "MNLF rampage under [International Humanitarian Law/Human Rights] guidelines."